(Joshua Roberts/Reuters Congressional Research Service is the respected in-house think tank for  lawmakers, who are encouraged to request research on areas of public policy that range from environmental protection to immigration.)

This post has been updated.

The secrecy that has traditionally surrounded Congress’s in-house think-tank is under fire from advocates of open government, who argue that the research conducted on major issues of public policy – from environmental protection to immigration – should at long last be made public.

For 101 years, the Congressional Research Service has conducted studies for members of the Senate and House, and the findings have remained confidential unless the lawmakers release the research themselves.

The aim is to allow senators and House members to pursue potentially controversial issues without fear of criticism from political opponents. Sometimes lawmakers request the studies; sometimes researchers do them in anticipation of congressional interest.

The secrecy of the work conducted by the 400 analysts of the CRS was underscored this fall in a “policy statement” circulated to staff, urging confidentiality to maintain good relations with lawmakers.

But a coalition of librarians, open-government advocates and advocates against wasteful spending, who are pressing for an end to what they call excessive secrecy in Congress’s research arm, which operates with a $100 million annual budget.

“We believe Congress should provide a central online source for timely public access to CRS reports,” a group of retired and former research service employees and dozens of open government groups wrote last week in a letter to Congressional leaders. “That would place all members of the public on an equal footing to one another with respect to access.”

The group said some support to members of Congress should remain under wraps through briefings and memos. But the advocates said the public is denied access to a large body of research that, while available to congressional staff, lobbyists and some journalists, through leaks “with no expectation of confidentiality,” never makes it to the public.

Under CRS policy, only with rare exceptions, such as when a report is given to a federal agency when the agency provided data used in the research, does the service distribute its findings. Congress does release a small number of reports every year — and they end up scattered over the Internet because they not easily able to be found in any one place (except CRS.gov, which is not available to the public).

The effort has the support of several lawmakers with an interest in open-government issues. Reps. Mike Quigley (D-Ill.) and Leonard Lance (R-N.J.) have introduced legislation that would direct the clerk of the House of Representatives to post the research service’s reports directly online to a publicly accessible site.

The campaign took on new urgency in the fall after the research service circulated a “policy statement” to its staff to solidify employees’ understanding of the mandate for confidentiality.

“Even in instances when a Member or committee publicly releases a confidential memorandum that CRS has prepared, staff may not provide copies of the memorandum to other congressional clients,” said the memo, obtained by the Federation of American Scientists and reported on the group’s Secrecy News Blog.

“You should answer any questions that [other] congressional clients have about the issue by preparing a new memorandum or other form of response […],” researchers were instructed, “but you must do so in a way that neither confirms nor denies that CRS did the work that has been made publicly available [by the Member or committee].”

Led by activist Steven Aftergood, the influential public interest group has long campaigned to open up CRS’s work to the public.

CRS communication director Ellis Brachman declined comment on the coalition’s letter or the memo.

Aftergood wrote that much of the memo is overwrought.

“Instead of confidentiality serving as a valuable means to an end, the new policy here elevates confidentiality into an end in itself, and in doing so casts doubt on the good sense of CRS management,” he wrote on the blog.

One CRS staffer, the memo said, had a request for data rejected by an agency legislative affairs office unless CRS identified the lawmaker who wanted the data. “You must never reveal the name of the congressional requester without the client’s express permission,” said the document, approved by Director Mary Mazanec. “In this case, you should explain to the executive branch agency that CRS’s statutory mission is to provide confidential research and analysis for the Congress, and that we cannot identify the requester.”